The goals of this application are to elucidate the cellular and intracellular molecular mechanisms by which the HIV envelope protein gp120 induces dysfunction and/or loss of peptidergic neurons in the brain, with emphasis on the most abundant peptidergic neuron, the neuropeptide Y (NPY) neuron. Two working hypotheses will be challenged. One, gp120 induces defective signal transduction and neuronal death in the brain of AIDS patients and this is due, in part, to an effect of gp120 on the neuron itself and/or other cells the secretory products of which regulate neuronal function. Two, gp120 induces a chronic expression of an inhibitory transcription factor complex of Fos/Jun within the NPY neuron and/or other cells regulating the NPY neuron, a consequence of which is defective signal transduction, e.g., impaired response to activation of the cAMP/protein kinase C pathways. An experimental model system of aggregate cultures derived from fetal rat brain is fully operative in our laboratory and will be used as a tool to achieve our goal. To validate that the rat model can serve as an alternative to the human, we will establish a culture system derived from the brains of human abortuses and conduct a parallel study of gp120 action in the human and rat models. S.A.1. Establish culture system as a guideline. S.A.2. Characterize the effects of the gp120 on the function/survival of the cultured NPY neurons: conduct a comparative study in the human and rat model systems. a) Define the time/dose kinetics of gp120 induction of dysfunction (response to forskolin and phorbol ester) and death of NPY neurons. b) Define the structure-function characteristics of gp120 actions: the role of gp41, the role of a VIP/CD4-like receptor and the requirement for specific regions of gp120. c) Ascertain if glial cells mediate the effects of gp120 on the NPY neurons. S.A. 3. Elucidate the intracellular molecular mechanisms of gp120-induced defective signal transduction, with emphasis on Fos/Jun family of transcription regulators. The results generated in these studies will provide insight into the mechanisms underlying gp120 actions in the human brain, which will serve as the baseline/guide for the design of therapeutic agents for future clinical management and possibly prevention of abnormalities expressed in the brains of HIV-infected people. An important and most timely outcome of this study will be the availability of an iv vitro reliable model system to test the efficacy of these newly designed therapeutic agents.